SwiftUI or UIKit for a new project
Pick one or the other is a tricky question. If a project is planned for a long term go with UIKit/AppKit. SwiftUI is a hot new thing right now and I think it needs to bake a cycle or two to stabilize, there will be changes and best practices only are just about to emerge.
If you need SwifUI features you can implement
UIViewControllerRepresentable to use SwiftUI in UIKit and use UIKit in SwiftUI use
All in all SwiftUI for short fun projects at the moment is a way to go, but I won’t bet on SwiftUI now, because it feels like Swift when it launched back in 2014.